1. Field of the Invention
This invention relates to the delivery of respiratory gases, and in particular to patient interfaces for providing gases to patients requiring respiratory therapy.
2. Summary of the Prior Art
In the art of respiration devices, there are well known a variety of respiratory masks which cover the nose and/or mouth of a human user in order to provide a continuous seal around the nasal and/or oral areas of the face such that gas may be provided at positive pressure within the mask for consumption by the user. The uses for such masks range from high altitude breathing (i.e., aviation applications) to mining and fire fighting applications, to various medical diagnostic and therapeutic applications.
One requisite of such respiratory devices has been that they provide an effective seal against the user's face to prevent leakage of the gas being supplied. Commonly, in prior mask configurations, a good mask-to-face seal has been attained in many instances only with considerable discomfort for the user. This problem is most crucial in those applications, especially medical applications, which require the user to wear such a mask continuously for hours or perhaps even days. In such situations, the user will not tolerate the mask for long durations and optimum therapeutic or diagnostic objectives thus will not be achieved, or will be achieved with great difficulty and considerable user discomfort.
Where such masks as those used above are used in respiratory therapy, in particular treatment of obstructive sleep apnea (OSA) using Continuous Positive Airway Pressure (CPAP) therapy, there is generally provided in the art a vent for washout of the bias flow or expired gases to the atmosphere. Such a vent may be provided for example, as part of the mask, or in the case of some respirators where a further conduit carries the expiratory gases, at the respirator. The washout of gas from the mask is essential to ensure that carbon dioxide build up does not occur over the range of flow rates. In the typical flow rates in CPAP treatment, usually between 4 cm H2O to 20 cm H2O, prior art attempts at such vents have resulted in excessive noise causing irritation to the user and concentrated flows of gases irritating any bed partners.
Various approaches have been developed in the prior art to attempt to reduce the noise by using slots to disperse the escaping gases when CPAP therapy is provided. For example, U.S. Pat. No. 6,460,539 and U.S. Pat. No. 3,890,966. However, these prior art methods are not entirely satisfactory in eliminating the extra noise created by a vent at the mask.